Derivative Instruments and Hedging Activities (Schedule of Gain or Loss on Derivative Contracts) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Net loss on fair value adjustments			$ (28,149)	$ (21,129)
Total loss on derivative contracts	$ (15,484)	$ (8,249)	(16,416)	(5,820)
Crude Oil [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gain on settlements	3,707	4,511	11,214	14,464
Net loss on fair value adjustments	(18,466)	(12,755)	(27,604)	(20,544)
Total loss on derivative contracts	(14,759)	(8,244)	(16,390)	(6,080)
Natural Gas [Member] \| Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net gain on settlements	310	454	519	845
Net loss on fair value adjustments	(1,035)	(459)	(545)	(585)
Total loss on derivative contracts	$ (725)	$ (5)	$ (26)	$ 260

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5618551-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (a),(c),(d),(e)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959

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Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

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